Radio receiver



E. L. BROWN RADIO RECEIVER June 4, 1940.

Filed Feb. 28, 1938 Patented June 4, 1940- I UNITED STATES PATENT OFFICE RADIO RECEIVER Elmer L. Brown, San Francisco, Galifl, assignor to Joseph B. Smith, San Francisco, Calif., as trustee Application February 28, 1938, Serial No. 193,112 3 Claims. (Cl. 250-20) This invention relates generally to radio reof a twin diode electron relay l1. This tube ceiving equipment, and particularly equipment makes use of the two anodes IB and I9, and the adapted for use with radiowaves of ultra high two heated cathodes 2| and 22. Theinput cirfrequencies, as for example from 30 to 60megacuit includes the inductance 23 which is tuned 5' cycles. More particularly it relates to that part by the variable condenser 24, and has its one 5" of the radio receiver including the detector and side connected to the anode l8, and its other side audio frequency amplifiers interposed between connected to the cathode 2|, through the conthe detector and a loud speaker or like translater. denser 25. Cathode 2| is shown connected to It is an object of the invention to provide a g un t r u h by-p c ndens r 6, nd

' receiver of the above character which will be the biasing resistor 21. Anode I9 is connected 10 characterized by quietness of operation, without to ground, While cathode .22 is connectedby consacrifice of selectivity or sensitivity. By quietductor 28, to the two resistors 29 and 30, which ness of operation I have particular reference to in r nnec re pec ively to one side of inabsence of parasitic noises such as are frequently ductance 23, and the cathode 2|. The heater experienced in such systems, freedom from local or heaters for cathodes 2| and 22 are supplied 15 alternating current hum, and comparative freewith current from some convenient source, as is dom from so-called diathermic interference. By well known to those skilledin the art. One side diathermic interference I have particular referf the heater Circuit can b u d d as illusence to interference caused by various pieces of e To S pp y a su t b e Source of B-battery high frequencyequipment, such as medical units. potential to the detector a s stor 3| con- A further object of the invention is to provide nects between the cathode 2| and the B-battery a novel form of resistance coupling to the input P ate Supply bus conductor 32. of an audio frequency amplifier, whereby pa A detector of the type described above will in d t f i noises r suppressed, effectively integrate or ole-modulate radio signal 25' Further objects of the invention will appear energy, and because of its stability it is par 25,

from the following description in which the pretieularly desirable W h u tra high frequencies ferred embodiment of. the invention has been set of the order m ntioned.

forth in detail in conjunction with they accom- The audio frequency amplifier |2 includes an panying drawing, I electron relay 33 of the triode type, having a The present invention makes use. of resistance P e anode a grid 35 d a Cathode 3 30.

coupling to the input'of an audio frequency am:- T input circuit for the amplifier l2 and the plifier, d thi coupling i h th t certain coupling between this input circuit and the outtypes of interfering impulses are suppressed. p t f the e e tor ll, is preferably as follows: Generally it is convenient to make use of this A p r f r i s 31 d are s a y n- 35. m of coupling between t t t of th di nected together, and are of exactly the same 35 frequency detector, and the, input of th first value. The end terminal of resistor 31 connects stage of audio frequency application, h am to the grid 35, and the end terminal of resistor type of coupling can be used in subsequentstages connects to ground, as for example o t e of audio frequency application, and as will be grounded bus eondlleter Which y be t e 46 presently pointed out, a limiter network or ream r Chassis f he Set. The cathode 36 is peater can be interposed between successive also Connected to r und thr ugh the resistor stages, 4|, which is shunted by the by-pass condenser Referring now to the circuit diagram constl- 42. serially connected between the cathode 22 tuting the single figure of the drawing, it illusof the e e to a d the mid-point 43 between 1 5' trates a radio receiver consisting generally of a resistors and are the blocking o denser 45 radio frequency amplifier In, a detect or d 44 and the variable resistor or potentiometer 46. modulator H and a stage [2, of audio frequency T precise manner i Wh ch his input circuit amplification having its input coupled to the outfor the amplifier and the p g afforded put of t t Following t di i to the detector, operate to suppress noise, will 5 quency amplifier |2 there is a limiternetwork be Subsequently s bed in detail.

I3, and this network supplies the last stage audio The limiter network l3 makes use of a multifrequency amplifier Hi. In a conventional sysgrid el r n r lay 3, h ving the plate or anode tem a loud speaker I6 is coupled tothe output 49, grids 50, 5| and 52, and heated cathode 53. of the amplifier M. The input circuit and the coupling between the The type of detector illustrated makes use input circuit of the network l3 and the output the other terminal connects to the resistors v80 and 6|. Resistor 6| connects to the grid 52, while resistor 60 connects to the grounded bus con-- Resistor 62 connects directly between ductor 39. grid 52 and the bus conductor 39.

The plate circuit for the limiter relay 48 in cludes the resistors 64 and which are connected in series between plate 49 and the B- battery bus conductor 32. Grid 5i also connects between resistors 64 and 65, and to ground through the resistor 66. The grid or suppressor 50 is shown conductively connected to the cathode 53, and both these elements are connected to ground through conductor 51.

The audio frequency amplifier I4 includes the electron relay S8, of the pentode type, which has an anode or plate 69, grids 10 and "H, and heated cathode 12. For coupling the input of this amplifier to the output of the limiter network I3, a pair of resistors 13 and 14 are provided, which serially connect between the grid El, and ground. These resistors are of equal value, and the connection between the same is connected to the plate 49 of the limiter relay 48, through the blocking condenser 16. The cathode 12 is connected to ground through the biasing resistor 11, which is shunted by the by-pass condenser 18.

Assuming that the last amplifier it operates a loud speaker I6, the plate circuit of relay 68 can include the transformer 19, the secondary of which is connected to the loud speaker IS.

The proper values for the resistors employed will depend upon various circuit characteristics, and the characteristics of the electron relays employed. As previously pointed out the resistors 31 and 38 should be of equal values, and this is likewise true of the resistors 59, SI, and 62 of the limiter network I3, and the resistors 13 and 14 of the audio frequency amplifier I4.

By Way of example, the various resistors can have specific values as follows: Referring first to the detector II, resistors 29, 30 and 3I have values of about 50,000 ohms, 0.5 megohm, and 50,000 ohms respectively. The biasing resistor 21 can be of the order of 10,000 ohms. With respect tothe audio frequency amplifier I2, and its coupling to the output of the .detector II, resistors 31 and 38 can. each be of the order of 0.1 megohm. Potentiometer 46 can have a range of resistance from zero to a maximum of about 1.0 megohm. Biasing resistor 4| can be of the value of about 1,000 ohms. Series resistors 59 and 60 carrying plate current to relay 33, can be of the order of 50,000 and 20,000 ohms respectively. With respect to the network I3 and its coupling to amplifier I2, resistors 6| and 62 can each be of the order of 50,000 ohms. Grid resistor'51 can be of the order of 50,000 ohms. Resistors 64 and 65 in the plate circuit of relay 48 can be of the order of 10 megohms and 50,000 ohms respectively. Resistor 66 can be of the order of 6,000 ohms. With respect to the last amplifier I 4 and its coupling to the output of network I3, resistors 13 and 14 can each be of the value of 1 megohm.-

.33, about 10 microfarads.

Biasing resistor 11 can be of the value of 450 ohms.

Proper values for the various by-pass condensers will be understood by those skilled in the art. For example the by-pass condenser 25 for the detector II can be of the order of .0001 microfarad. By-pass condenser 26 of. the order of 0.1 microfarad. Coupling condenser 44 can be of the order of 0.1 microfarad, and by-pass condenser 42 for the audio frequency amplifier relay Coupling condenser 56 can be of the order of 1 microfarad, and coupling condenser 16 about 0.01 microfarad. By-pass condenser 18 for the last amplifier relay can be about 10 microfarads.

The B-battery source for the various relays can be a battery, but in most instances will consist of a rectifier 8I,.operating from alternating current supply lines, together with a filter 82.

Operation of the system described above, can be' outlined as'follows: De-modulated or integrated signalv energy from the detector II is impressedupon the. grid 35 of the audio frequency amplifier I2, through the coupling condenser 44, the variable resistor 45 and resistor 31. Amplified and corresponding current variations in the output of amplifier I2, are repeatedthrough the limiter network I3, and impressed upon the grid circuit for the final audio frequency amplifier. The variable resistor 40 constitutes a volume control, whereby the intensity of current variations applied to the amplifier I2 can be adjusted over a wide latitude, thus adjusting the sound level of the loud speaker I t for signal energy of a given strength. a

In operating a radio receiver upon ultra high frequencies, as for example from 30 to GO-megacycles, so-called diathermic interference is always a troublesome factor. Medical and other high frequency units operate generally within this range of frequencies, and frequently such equipment is not properly designed, or properly shielded to prevent radiation. It is typical of such interference that it is. modulated by a 60 cycle hum, and with the usual type of ultra high frequency radio receiver, this hum will cause interference over a relatively wide range of frequencies, and will drown out reception of a de sired signal. According to my observations this typeof interference is due to a large measure to the fact that the audio frequency amplifier of such receivers are not only sensitive to pulsations of the desired signal energy, but are also unduly sensitive'to interfering impulses such as cause or accompany noisy reception as describedabove. Interference of the type which I particularly desire to nullify or suppress, acterized by a distortion of the audio frequency Wave form, and this'has the effect of making the amplifier system extremely noisy over a relatively wide band of frequencies. Even though the interfering frequency may not of itself be relatively broad, the noise produced in-the loud speaker can be had over a relatively wide range of tuning, thus making it difficult if not impossible to properly receive signals above the noise level.

appears to be char- Referring now to the amplifier I2, since re- 3 sistors 31 and 38 applied from'the equally between the resistors 31 and 38. Al-

though'resis-tor 38 is connected to what is nor-' mally a point of neutral potential, momentary interfering impulses of the type'referred to above cause momentary shift in the potential applied are equal in value, potentials output of detector II, to point whether positive or negative in sign, divide nected to the same,

to the cathode 36, because of the connection of this cathode to the grounded bus conductors 39, through resistor 4|. Thus for such momentary interfering impulses, the momentary potential difference between cathode 36 and grid is such as to not cause a corresponding current variation in the plate current. In other words with this amplifier the signal energy on the positive side of the cycle is properly impressed upon the grid 35 to cause corresponding amplifier current variations in the plate circuit. However, abnormal interfering potential variations such as cause noisy reception with a 60 cycle hum are nullified. With respect to the suppressor I3, the relay 48 and the input and output circuits con- .are designed to limit the maximum intensity of impulses repeated to the input circuit of the final amplifier M. The audio frequency amplifier l4 because of the equal resistors I3 and 14, likewise serves to minimize the noise and interference of the type previously described.

Because of the action described above, the noise level produced by diathermic machines is greatlylowered without lowering the sensitivity of the receiver to radio signal energy. At the same time such interference is relatively sharply localized upon the tuning dial, so that radio signal energy of a frequency not far remote from the principal frequency of the interference, can be tuned in without difficulty.

The limiter network I3 can be omitted if desired, in which event the output of amplifier l2 can be directly coupled to M. However, as previously pointed out the limiter network is desirable in suppressing momentary potential impulses, which would otherwise be of relatively high intensity compared to the signal impulses. Briefly, this limiter network operates as follows: Normally the plate cathode'impedance of relay 4B is relatively high, for the desired signal energy. When an interfe'ring impulse of considerable intensity, greater than that of the signal energy, is impressed upon grid 52 through resistor 6|, the plate cathode potential is immediately lowered to a relatively low value, during the duration of the impulse, whereby such impulse is not effectively repeated to the input of the last relay l4.

I claim:

1. In a radio receiver, a detector of radio frequency signals, an audio frequency amplifier, said amplifier including an electron relay having anode, grid and cathode elements, and means forming a noise suppressing resistance coupling the input of amplifier between the output of the detector and the input of the amplifier, said means including a pair of grid resistors connected in series between the grid and ground, a biasing resistor connected between the cathode and ground, the first mentioned pair of resistors being of equal values, and a connection to the mid-point between the resistors from the output of the detector, for applying potentials from the detector to the amplifier.

2. In a radio receiver, a detector of radio frequency signals, an audio frequency amplifier, said amplifier including an electron relay having anode, grid and cathode elements, and means forming a noise suppressing resistance coupling between the output of the detector and the input of the amplifier, said means including a pair of grid resistors of equal values connected in series across the grid and ground, a biasing resistor connected between the cathode'and ground, and means forming a. connection between the output of the detector and the mid-point between the first named resistors, for applying potentials from the output of the detector to the amplifier, said last means including in series with the same a variable resistor and a blocking condenser.

3. In a radio receiving system, a radio frequency detector, an audio frequency amplifier, said amplifier including an electron relay havingv anode, grid and cathode elements, noise suppressing means serving to couple the output of the detector to the input of the amplifier, said last means including a pair of resistors each of equal value connected in series across the grid and ground, a resistor connected between the cathode and ground, anda connection between the output of the detector and the midpoint between the first two named resistors, said connection serially including a blocking condenser and a variable resistor, a limitor network having its input coupled to the output of the audio frequency amplifier, a second audio frequency amplifier, and a noise suppressing coupling between the input of the last named amplifier and the output of the lirnitor network, said last named means including a pair of resistors of equal value-connected in series between the grid of the last mentioned relay and ground, a resistor connected between the cathode and ground, and a connection including .a blocking condenser between the output of the network and the midpoint between the resistors of equal value.

ELMER L. BROWN. 

